Optical glass and process for its manufacture

ABSTRACT

OPTICAL GLASS COMPOSITIONS COMPRISING 25 TO 65 WT. PERCENT SIO2, 4-35 WT. PERCENT K2O, 4-45 WT. PERCENT TIO2 AND 3-45 WT. PERCENT SB2O3, CHARACTERIZED IN THAT THE MINIMUM CONTENT OF TIO2 PLUS SB2O3 AMOUNTS TO 18 WT. PERCENT.

United States Patent 3,589,918 OPTICAL GLASS AND PROCESS FOR ITS MANUFACTURE Walter Jahn, Ingelheim, Germany, assignor to JENAer Glaswerk Schott & Gem, Mainz, Germany No Drawing. Filed Nov. 1, 1968, Ser. No. 773,374 Claims priority, application Germany, Nov. 14, 1967, P 15 96 864.6 Int. Cl. C03c 3/04 U.S. Cl. 106-53 15 Claims ABSTRACT OF THE DISCLOSURE Optical glass compositions comprising 25 to 65 wt. percent SiO 435 wt. percent K 0, 4-45 wt. percent TiO and 3-45 wt. percent Sb O characterized in that the minimum content of TiO;,, plus Sb O' amounts to 18 wt. percent.

This invention relates to optical glass compositions and has particular reference to glasses which at relatively low indices of refraction have dispersion values greater than that of conventional flint glass and to a process of making the same.

For the manufacture of well-corrected lens systems, crown glasses are required together with flint glasses which at relatively low indices of refraction have a dispersion that is greater than that of conventional flint glasses. Glasses of this type, which are referred to as low flints, contain more or less large amounts of titanium oxide, which contributes greatly towards increasing the dispersion. Flint glasses containing titanium oxide are already known, both with a phosphate base and with a silicate base. Phosphate glasses containing titanium oxide provide compositions which exhibit generally, more extreme optical values as regards high dispersion combined with the lowest possible refraction. Examples of the latter phosphate glasses containing titanium oxide are the glasses disclosed in German Pat. No. 939,531.

However, the melting of such glasses as required in connection with their production is difiicult and complicated because of the relatively low resistance to devitrification of these compositions. Silicate-base low flints, which are conventionally prepared on a basis of the well-known three-component system of SiO -Na O-TiO exhibit optical values that ditfer only slightly from those of conventional lead silicate-base flint glasses. It is known that the addition of fluoride can improve the optical values, the same having been described, for instance, in German Pat. No. 973,350. The state of the art does permit the manufacture of optical glasses containing fluoride, but to do so one must accept the fact that the process of the manufacture of such glasses is an extremely costly one.

One of the primary objects of the invention is to provide novel glasses which at relatively low indices of refraction have a dispersion which is greater than that of conventional flint glasses.

Another object is to provide glasses of the above nature which are free of fluorine and are characterized by low cost of manufacture.

Other objects and advantages of the present invention will become apparent from the following description.

The above objects are achieved by the finding of a new field of glasses comprising 2565 wt. percent SiO 4-35 wt. percent K 0, 4-45 wt. percent TiO and 3-45 wt. percent Sb O in which the sum of the percentages of Ti0 plus Sb O amounts to at least 18 wt. percent.

The maximum amounts of the other components change somewhat according to the percentages of K 0, the percentage of TiO, being limited by the incipient crystallization (devitrification) area and the percentage of Sb O being limited by the increasing yellow-brown discoloration thereby produced which would eventually prevent the use of these glasses for optical purposes.

Accordingly, at a K 0 content of up to 15%, the maximum percentage of Ti0 amounts to 35%, and that of Sb O amounts to 45 At a K 0 content of above 15%, the maximum percentages of TiO and Sb O amount to 45% and 38% respectively.

The K 0 can be replaced wholly or partially by Na O although the optical values obtained are then less extreme. Additionally, the color and stability of the glasses may be impaired.

PbO is suitable for varying the range of the optical values within relatively wide limits, the content thereof can amount to as much as 40%. In particular, it permits the dispersion to be increased and the T102 content to be diminished.

MgO, C30, B30, Z110, B203, A1203, AS203,

- Nb O Ta O and W0 individually or in mixtures, and

in quantities of up to 8% are particularily suitable for varying the range of the optical values within narrower limits.

Glasses having high TiO or Sb O contents may exhibit an undesirable strong yellow or brown coloration. The intensity of this color can be greatly reduced by the addition of oxidizing substances during the melting, such as for example, sodium arsenate. Further the introduction of oxygen or other oxidizing gases during the melting can improve the color.

The following example will serve to illustrate the invention and in particular a method of a simple and efficient nature for producing the novel glasses of the invention. The same is given by way of illustration only and should not be construed as limitative of the invention.

EXAMPLE A batch of 1000 grams, comprised of 570 g. SiO g. TiO- g. Sb O 100 g. K 0 (in the form of K CO and 5 g. of Na HAsO was placed in a ceramic crucible and heated to a temperature of about 1460 C. in an electrically heated or gas heated furnace. After the batch had fused it was refined for one hour at 1500 C. The glass was then stirred for about one hour, while the furnace was cooled down to 1460 C. The glass was thereafter poured at 1440 C. into a preheated iron mold and then transferred to a lehr which was at a temperature of 550 C. and was cooled at a rate of about 7 per hour down to room temperature.

'In the table which follows, examples of glasses according to the invention have been set out. All mounts specified are percentages by weight.

These glasses all show good resistance to weather and to acids.

What is claimed is:

1. An optical glass composition consisting essentially of 25-65 wt. percent S 4-35 wt. percent K 0, 4-45 wt. percent TiO and 345 Wt. percent Sb O in which the sum of the percentages of TiO and Sb O amounts to at least 18 wt. percent.

2. Optical glass of claim 1 in which at a K 0 content of up to wt. percent, the content of TiO does not exceed 35 wt. percent and that of Sb O does not exceed 45 wt. percent.

3. Optical glass of claim 1 in which at a K 0 content exceeding 15 wt. percent, the content of T102 does not exceed 45 wt. percent and that of Sb O does not exceed 38 Wt. percent.

4. Optical glass of claim 1 in which at least a part of the K 0 is replaced by Na O.

5. Optical glass of claim 1 containing additionally up to 40 Wt. percent PbO.

6. Optical glass of claim 1 containing at least one member selected from the group consisting of MgO, CaO, SrO, B30, Z110, B203, A1203, AS203, Nb O5, T3205 and W0 in an amount of up to 8 Wt. percent.

7. Optical glass of claim 1 containing 7 Wt. percent K 0, 40 wt. percent Sb O 40 wt. percent SiO and 13 wt. percent TiO 8. Optical glass of claim 1 containing 10 wt. percent K 0, 7 wt. percent Sb O 62 wt. percent SiO and 21 wt. percent TiO 9. Optical glass of claim 1 containing 19 wt. percent K 0, 3 wt. percent Sb O 33 wt. percent S10 and 45 wt. percent TiO 10. Optical glass of claim 1 containing 20 Wt. percent K 0, 38 wt. percent Sb O 31 wt. percent SiO and 11 wt. percent T10 11. Optical glass of claim 1 containing wt. percent coco g K 0, 10 Wt. percent Sb O 25 wt. percent SiO and 40 wt. percent T10 12. Optical glass of claim 4 containing 10 wt. percent Sb O 50 Wt. percent SiO 21 wt'. percent TiO- and 19 wt. percent Na O.

13. Optical glass of claim 5 containing 4.8 wt. percent K 0, 14.3 wt. percent Sb O 38.1 Wt. percent SiO 4.8 wt. percent TiO and 38 wt. percent PbO.

14. Optical glass of claim 6 containing 27 wt. percent K 0, 3 wt. percent Sb O 28 wt. percent SiO 40 wt. percent TiO and 2.0 wt. percent A1 0 15. The method of manufacture comprising the steps of preparing a glass batch consisting essentially of 25-65 wt. percent SiO 4-35 wt. percent K 0, 4-45 wt. percent T10 and 345 wt. percent Sb O in Which the sum of the percentages of TiO and Sb O amounts to at least 18 Wt. percent, heating said batch at a temperature and for a period sufiicient to melt the ingredients thereof and produce a homogeneous glassy structure, annealing said structure at a lower temperature and slowly cooling said structure to room temperature, to thereby produce a clear durable transparent optical glass.

References Cited UNITED STATES PATENTS 2,838,408 6/1958 Rindone 106-53 2,861,001 11/1958 Rindone 106-53 FOREIGN PATENTS 1,271,757 12/1966 Germany 106-52 ROBERT D. EDMONDS, Primary Examiner US. Cl. X.R. 

